A motor vehicle powertrain includes a prime mover to generate torque, a transmission coupled to the prime mover to leverage the torque, and a drivetrain coupled to the transmission to distribute the torque to wheels of the vehicle. For example, the drivetrain of some vehicles includes a transfer case to carry out changes from a two-wheel-drive (2WD) mode to a four-wheel-drive (4WD) mode and vice versa, or changes from a high range 4WD mode to a low range 4WD mode and vice versa.
An example of a multi-speed transfer case includes a housing, an input to receive torque, an output to transmit torque, and a planetary gear set between the input and the output. The gear set includes a helical sun gear connected to the input, a planetary carrier connected to the output and carrying helical pinion gears in mesh with the sun gear, and a helical ring gear in mesh with the pinion gears and grounded to the housing. A method of operating the transfer case includes driving torque in to the sun gear, connecting the sun gear to the output in a two-wheel drive mode and in a four-wheel-drive high range mode to drive torque out of the sun gear according to a direct drive ratio, and connecting the carrier to the output in a four-wheel drive low range mode to drive torque out of the carrier according to an under drive ratio of about 2.64.